The present invention relates to a high-speed optical memory element. In order to increase speed of a memory element, optical pulse is recorded and read all-optically without conversion into electrical signal at very high speed. Optically-induced spin accumulation is used for recording the ferromagnetic metal embedded into optical waveguide operates as a high speed memory element. The ferromagnetic metal is sandwiched between a conductor on one side and a tunnel barrier followed by a conductor on the other side. The voltage is applied between two conductors. For data recording, the optically induced spin-polarized tunneling and spin accumulation is used. The optically induced spin-polarized tunneling occurs due to absorption of circularly polarized light. The torque of accumulated spin reverses magnetization of ferromagnetic metal. For reading Faraday rotation or non-reciprocal loss/gain in semiconductor-ferromagnetic-metal hybrid is used.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A non-volatile optical memory element comprises: an optical waveguide, which has a core region embedded between two cladding regions, wherein a refractive index of the core region is higher than that of the cladding regions, a ferromagnetic-metal region embedded inside the cladding region or the core region, a non-conductive tunnel-barrier region interposed between a first conductive region and a second conductive region, wherein the ferromagnetic-metal region is interposed between the first conductive region and the tunnel-barrier region followed by the second conductive region, and the ferromagnetic-metal region is close enough to the waveguide core region in which light propagating in the waveguide penetrates into the ferromagnetic metal region, and a size and form of the ferromagnetic metal region is adjusted so that the ferromagnetic metal region is in a single-domain state, and data is stored in the memory element in two opposite directions of magnetization of the ferromagnetic-metal region.
2. A recording method of a circularly-polarized pulse into the memory element according to claim 1 , by reversal of magnetization ferromagnetic-metal region due to an arrival optical pulse, the method comprising the following steps: applying negative voltage to the first conductive region and positive voltage to the second conductive region so that without illumination of light, the tunneling from the ferromagnetic-metal region into second-conductive region is small; illuminating the memory element by a circularly-polarized pulse by coupling input light pulse into the optical waveguide; exciting the electrons by the circularly-polarized optical pulse in the ferromagnetic-metal region to higher energy level, wherein polarization of the optical pulse is such that the excited electrons are of the same spin polarization or up-spin, and the excited up-spin electrons tunnels from the ferromagnetic-metal region into the second-conductive region; making non-spin-polarized electrons, said both up-spin and down-spin electrons, flow from the first-conductive region into the ferromagnetic-metal region; accumulating down-spin electrons in the ferromagnetic-metal region; and reversing magnetization of the ferromagnetic-metal region due to torque of accumulated down-spin electrons.
3. A recording method of a circularly-polarized pulse into the memory element according to claim 1 by reversal of magnetization ferromagnetic-metal region due to an arrival optical pulse, the method comprising the following steps of: applying positive voltage to the first conductive region and negative voltage to the second conductive region so that without illumination of light, the tunneling from ferromagnetic-metal region into second-conductive region is small; illuminating the memory element with a circularly-polarized input pulse by coupling input light pulse into the optical waveguide; exciting the electrons by the circularly-polarized optical pulse in the second-conductive region to higher energy level, wherein polarization of the optical pulse is such that the excited electrons are of the same spin polarization or up-spin and the excited up-spin electrons tunnels from the second-conductive region into the ferromagnetic-metal region; making non-spin-polarized electrons, said up-spin and down-spin electrons, flow from the ferromagnetic-metal region into the first-conductive region; accumulating up-spin electrons in the ferromagnetic-metal region; and reversing magnetization of the ferromagnetic-metal region due to torque of accumulated up-spin electrons.
4. The non-volatile optical memory element according to claim 1 , wherein the ferromagnetic metal region contains at least one of transition metals (Cr, Mn, Fe, Co, or Ni) and their alloys; the first conductive region is made of a semiconductor with p-type doping; and the second conductive region is made of semiconductor with n-type doping.
5. The non-volatile optical memory element according to claim 4 , wherein the tunnel barrier region is formed by Schottky contact between the ferromagnetic metal region and a semiconductor with n-type doping.
6. The non-volatile optical memory element according to claim 1 , wherein the ferromagnetic region contains at least one of transition metals (Cr, Mn, Fe, Co, Ni) and their alloys; the first conductive region is made of a semiconductor with p-type doping; and the second conductive region is made of semiconductor with p-type doping.
7. The memory elements according to any one of claims 1 , and 4 – 5 , further including a reading waveguide path, wherein the reading waveguide path is directed perpendicularly to a direction of magnetization of ferromagnetic metal, an optical waveguide of reading path has a core region embedded between two cladding regions, a refractive index of the core region is higher than that of cladding regions, the ferromagnetic metal region is formed inside the waveguide cladding region, the optical gain is provided by an active region formed inside the waveguide core layer, gain is adjusted so that for one direction of magnetization, the light is absorbed and for opposite direction of magnetization, the light is amplified, and depending on data stored in the memory element, the light passes through reading waveguide path or is stopped.
8. The memory elements according to any one of claims 1 , 4 – 5 , further including a reading waveguide path, wherein the reading waveguide path is directed along a direction of magnetization of ferromagnetic metal, an optical waveguide of reading line having a core region embedded between two cladding regions, a refractive index of the core region is higher than that of cladding regions, the ferromagnetic metal region is formed inside waveguide cladding region region, the pulse passing memory element undergoes the polarization rotation due to Faraday effect of ferromagnetic metal and a direction of the polarization rotation corresponds to the magnetization direction of ferromagnetic metal.
9. The memory device containing the memory elements according to any one of claims 1 and 4 – 5 , further including delay elements, an input waveguide path, and a clock-pulse waveguide path.
10. The memory device according to claim 9 wherein optical gain is provided for the input and the clock-pulse waveguide paths.
11. A memory device containing the memory elements according to claims 10 having elements for recording, further including elements for reading, which includes delay elements, an output waveguide path and a clock-pulse waveguide path, wherein the clock pulse is coupled into each memory element, passing through each memory element and coupled into output waveguide path by connecting the output waveguide path and the clock-pulse waveguide path to each memory element, and from one memory element to next memory element, the clock pulse is delayed for time period equal to the period of pulses of output pulse train, so that depending on data stored in a memory element, the clock-pulse passes through the memory element or is stopped and the sequence of pulses in pulse train corresponds to data stored in memory cells.
12. The memory element according to claim 11 , wherein a reading waveguide path and a recording waveguide path utilize the same waveguide.
13. The memory element according to claim 11 , wherein ferromagnetic metal is formed inside waveguide core region.
14. Memory device containing the memory elements according to claims 11 having elements for recording, further including elements for reading, which includes delay elements, output waveguide path, clock-pulse waveguide path, analyzer, polarizer and polarization rotator, an axis of analyzer is perpendicular to an axis of the polarizer, the rotation angle of the polarization rotator is adjusted to be the same as a polarization rotation angle for light passing for reading waveguide path of a memory element, a clock pulse passing polarizer is coupled into clock-pulse waveguide path, delayed clock pulse passing reading waveguide path of each memory element is coupled into an output waveguide path, an output pulse train is obtained by the polarization rotator followed by the analyzer, from one memory element to next memory element, the clock pulse is delayed for time period equal to the period of pulses of output pulse train, for memory cells, where a direction of polarization rotation is opposite to rotation by polarization rotator, the pulse passing memory element and polarization rotator has zero angle of polarization rotation as a whole, such pulse is stopped by the analyzer, for memory cells, where a direction of polarization rotation is the same as a rotation by the polarization rotator, the pulse passing memory element and polarization rotator have non-zero angle of polarization rotation as a whole, and such pulse passes through the analyzer so that the sequence of pulses in pulse train corresponds to data stored in memory cells.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
July 5, 2005
January 30, 2007
Browse 5M+ US patents with plain-English claim translations and AI-generated analysis.